Gauge and system for gauging fuel in an aircraft tank

Abstract

One aspect of the invention relates to an aircraft fuel gauge (20) which is intended to be located inside an aircraft fuel tank (10), the fuel gauge (20) being configured to form at least one capacitor (C1) with a fuel in the fuel tank (10), the fuel acting as a dielectric of the capacitor (C1), the fuel gauge (20) comprising at least one memory (212) and a microprocessor (211), the microprocessor (211) being configured to: - convert (51) a measured analogue capacitance value of the capacitor into a digital capacitance value; - calculate (52) a fuel height in the fuel tank (10) from the digital capacitance value and a predetermined dielectric constant of the fuel stored in the memory (212) of the fuel gauge (20); - store (53), in the memory of the fuel gauge (20), the calculated fuel height; - transmit (54) the calculated fuel height to a computer in a digital signal.

Description

DESCRIPTION TITLE: Fuel gauge and gauging system in an aircraft tank TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of aeronautics.

[0002] The present invention relates to an analog-to-digital conversion device for sensor data in a vehicle fluid tank and, in particular, but not limited to, for fuel gauging data in an aircraft tank. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] Monitoring the fuel content in an aircraft's tank is of paramount importance during flight. Therefore, it is essential to be able to track the quantity and density of the fuel in the tank in real time with a high degree of accuracy during flight.

[0004] To achieve this, it is known to install suitable sensors, such as gauges, densimeters and / or thermometers, in fuel tanks. Such sensors are connected to measuring electronics, located outside the tank, via a harness extending through a tank wall.

[0005] However, such a fuel tank constitutes a particularly difficult environment, notably forming an explosive atmosphere due to fuel vapors, which leads to significant constraints in the choice of the type of sensors as well as their functionalities and controls.

[0006] Usually, these sensors are of the analog and passive type, excited at low power levels, so as not to risk having a component that could overheat or, in case of fault, generate a spark.

[0007] However, they require the use of a harness very well protected by electrostatic shielding, with a highly sophisticated design and complex routing to minimize capacitance that interferes with the main data acquisition. This is the main known drawback of this type of gauging. It also requires a significant number of wires with point-to-point excitation of the sensors, as well as a common shielded connection for the measurement from the computer.

[0008] For these reasons, some fuel gauges incorporate capacitance-to-digital converters (CDCs), mounted directly on the gauge body. These CDCs measure the capacitance of the capacitor formed by the gauge and the fuel, convert it into a digital signal, and transmit it in digital format to the computer located outside the fuel tank.

[0009] Digital gauging has the advantage of directly converting capacitance values ​​in situ, which makes it possible to eliminate parasitic capacitances (related, among other things, to the wiring between the gauge and the computer) or other disturbances to obtain increased accuracy.

[0010] However, it does not solve the problems of increased dispersion of fuel characteristics important for gauging, severe environmental constraints in the tank, and insufficient maintenance data.

[0011] First, the arrival of sustainable aviation fuel (SAF) is disrupting historical gauging strategies, whereas fuel properties were previously stable and based on the use of the most common fuel, Jet A1 kerosene. Indeed, the gradual introduction of SAF as a replacement or supplement to JET A1 grade fossil kerosene is leading to a change in the important characteristics of the fuel with regard to the accuracy of fuel quantity measurement, namely the dielectric constant and the fuel density as a function of its temperature.

[0012] The disparity of possible fuels within an aircraft leads to errors due to the approximation resulting from the extrapolation of a fuel height based on a capacity measurement and the use of the typical dielectric constant of the single JET A1 for the entire aircraft.

[0013] It has been proposed to correct each measurement using processing algorithms in the gauging calculator, but this leads to complicating the method of determining the quantity and therefore the demonstrations of gauging accuracy, with risks of implementation errors, in non-nominal cases for example.

[0014] Furthermore, fuel gauges are subjected to a harsh environment, consisting of aircraft structural tanks: The beach and temperature variations are significant there. The constant presence of humidity due to the condensation of water vapor entering through the vents during descent, Potential fungal and bacterial contamination at the air-fuel interface in case of improper drainage operation

[0015] Capacitive strain gauges are sensitive to parasitic capacitance at terminal blocks and wiring harnesses. This parasitic capacitance can be generated by the conditions described above, for example through corrosion at the connections. The resulting capacitance faults can be permanent but are often transient, such as when temperature or vibration contributes to the fault's occurrence.

[0016] Capacity faults typically lead to undesirable cockpit effects such as incorrect fuel quantities exceeding nominal accuracy, or even false alarms. To mitigate this, gauge computers continuously provide gauge capacity information to the avionics.

[0017] This information can be used by aircraft maintenance systems to confirm a gauge / harness fault before opening the tank and removing the gauge or harness suspected of being faulty.

[0018] The gauge is then sent for maintenance to a repair shop, where a visual inspection followed by a functional test is performed at laboratory temperature, in accordance with the gauge's maintenance manual. This test may consist of measuring the gauge's capacity in air, and then measuring it when fully immersed in a fuel with a known dielectric constant. If the measured capacity values ​​are as expected, the gauge is declared fit for service and returned to the customer. It will be recorded by customer service as "No Fault Found."

[0019] In the case of intermittent faults, this process proves insufficient to trap parasitic capacitance faults. Even if the maintenance computers Centralized aircraft systems are generally capable of recording the history of capabilities seen by this gauge when it was installed in the aircraft, as well as important parameters such as, for example, the fuel temperature history in the tank; this information is not or rarely transmitted to the gauge repair shop, which makes diagnosing this type of fault laborious, if not impossible.

[0020] Therefore, there is a need to offer a digital gauging system that does not have the drawbacks of the current state of the art. SUMMARY OF THE INVENTION

[0021] The invention offers a solution to the problems mentioned above, by allowing digital gauging directly at the gauge level and therefore at the capacity measurement level, and easier maintenance by having the ability to store measurements and data related to these measurements directly at the gauge level.

[0022] Thus, the invention relates to an aircraft fuel gauge intended to be located inside an aircraft fuel tank, the fuel gauge being configured to form at least one capacitor with fuel in the tank, the fuel acting as the dielectric of the capacitor, the fuel gauge comprising at least one memory and one microprocessor, the microprocessor being configured to: Convert a measured analog value of capacitor capacitance into a digital capacitance value. Calculate the fuel level in the tank, based on the numerical value of the capacity and a predetermined dielectric constant of the fuel stored in the fuel gauge's memory. Store the calculated fuel level in the fuel gauge's memory. To transmit, in a digital signal, the calculated fuel level to a computing computer.

[0023] Thanks to the invention, it is possible to obtain a high level of reliability in fuel measurement by calculating the fuel level directly in the tank and by the gauge which includes a microprocessor. This allows a reliable measurement to be sent to a computer external to the tank, thus facilitating the management of a plurality of measuring gauges when the aircraft gauging system includes several gauges and the computer manages these several gauges.

[0024] Furthermore, the invention improves fuel gauge maintenance by giving the maintenance operator access to the data calculated by each gauge, allowing identification of any gauge anomaly without having to test it, thereby eliminating the problem of the gauge anomaly not reproducing during testing, due to the intermittent nature of the anomaly.

[0025] In addition to the characteristics just mentioned in the previous paragraph, the gauge according to an aspect of the invention may have one or more complementary characteristics from among the following, considered individually or according to all technically possible combinations.

[0026] In one embodiment, the memory is non-volatile memory.

[0027] In one embodiment, the memory is an electrically erasable and programmable read-only memory "EEPROM".

[0028] Another aspect of the invention relates to an aircraft fuel gauging system comprising: An aircraft fuel tank, At least one fuel gauge according to the invention located inside the fuel tank, A computing computer included in the aircraft and located outside the fuel tank, configured to: Receive the digital signal including the calculated fuel level, Calculate, from the fuel height and a predetermined tank geometry, a quantity of fuel in the tank.

[0029] In addition to the characteristics mentioned in the preceding paragraph, the system according to one aspect of the invention may have one or more additional characteristics from the following, considered individually or according to all technically possible combinations.

[0030] In one embodiment, the system further includes a thermometer inside the fuel tank.

[0031] Another aspect of the invention relates to an aircraft comprising the system according to the invention.

[0032] Another aspect of the invention relates to a method for measuring the quantity of fuel implemented by a system according to the invention, the method comprising: Convert, using the fuel gauge microprocessor, a measured analog value of capacitor capacitance into a digital capacitance value. Calculate, using the fuel gauge's microprocessor, the fuel level in the tank, based on the numerical value of the fuel's capacity and a predetermined dielectric constant stored in the fuel gauge's memory. Store the calculated fuel level in the fuel gauge's memory. To transmit, in a digital signal, the calculated fuel level to a computing computer, To receive, via the computing computer, the digital signal including the calculated fuel level, Calculate, using the computer, from the fuel height and a predetermined geometry of the tank, a quantity of fuel in the tank.

[0033] In another embodiment of the process, the predetermined dielectric constant is calculated by: Obtaining a temperature reading from the temperature sensor, Calculation of the predetermined dielectric constant from a dielectric constant of the fuel and the temperature obtained.

[0034] In one embodiment, the process further comprises: Store, in the fuel gauge memory, a data history including at least one of the following data: capacity, capacity standard deviation over a given period, fuel temperature, predetermined dielectric constant, calculated dielectric constant.

[0035] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0036] The figures are presented for illustrative purposes only and are in no way limiting to the invention. Figure 1 shows a schematic representation of a system comprising a gauge according to the invention, Figure 2 shows a schematic representation of a gauge according to the invention, Figure 3 shows a schematic representation of a system comprising a plurality of gauges according to the invention, Figure 4 shows a schematic representation of a fuel gauging method according to the invention, Figure 5 shows a schematic representation of a capacitor in a fuel gauge according to the invention, Figure 6 shows nomograms for determining an aircraft fuel dielectric constant as a function of fuel temperature. DETAILED DESCRIPTION

[0037] Unless otherwise specified, the same element appearing on different figures has a unique reference.

[0038] Figure 1 shows a schematic representation of a system S1 comprising a gauge 20 according to the invention. The gauge 20 according to the invention makes it possible to obtain a digital measurement of the fluid height in the fluid reservoir in which it is placed.

[0039] The system S1 shown in Figure 1 comprises a tank 10, a gauge 20 according to the invention, a computing computer 30 and an electrical harness 40, connecting the computing computer 30 to the gauge 20.

[0040] The tank 10 comprises walls defining a substantially closed internal space containing fuel. The density of the fuel is likely to vary depending on altitude, temperature and / or the filling level.

[0041] At least part of the gauge 20 forms a capacitor C1 with the fuel acting as a dielectric. For this purpose, the gauge 20 comprises a first electrode and a second electrode, for example, cylindrical, concentric, and arranged vertically. Specifically, the first electrode may be an external electrode and the second an internal electrode. The first and second electrodes define an annular space between them, in which the fuel rises during refueling and falls during consumption. The fuel level in the annular space thus modifies the capacitance of capacitor C1. In particular, the capacitance of capacitor C1 varies linearly with the fuel level in the internal space.

[0042] Capacitor C1 provides an analog capacitance measurement across its terminals, i.e., its electrodes. Gauge 20 further includes electronics 21 adapted to connect to the terminals of capacitor C1, preferably reversibly, i.e., with a removable connection means. For example, gauge 20 includes two connection means, each adapted to connect to one of the two electrodes of capacitor C1. Removable connection means are, for example, screws. The removable connection means are connected to the electronics 21 via connecting means, for example, sheathed electrical cables 22a and 22b shown in Figure 2.

[0043] The electronics 21 include a microprocessor 211 and a memory 212. Thus, the gauge 20 includes at least the microprocessor 211 and the memory 212, which stores instructions that, when executed by the microprocessor 211, cause the microprocessor 211 to implement the step associated with those instructions. Therefore, when an action is performed by the microprocessor 211 or the gauge 20, the microprocessor 211 of the gauge 20 executes instructions stored in memory 212 or in another memory of the gauge.

[0044] The microprocessor 211 is configured to perform part of the gauging process according to the invention. Preferably, the memory 212 is a non-volatile memory. Even more preferably, the memory 212 is an electrically erasable and programmable read-only memory of the "EEPROM" type.

[0045] The gauging method 5 according to the invention is schematically represented in Figure 4. This method 5 comprises at least five steps 51 to 55.

[0046] A first step 51 is performed by the microprocessor 211 of the gauge 20 and is a step of converting a measured analog value of the capacitance of capacitor C1 into a digital capacitance value. For this, the microprocessor 211, being electrically connected to capacitor 21, performs the actions of receiving the measured analog capacitance and then converting it into a digital value. In a preferred embodiment, this first digital capacitance value is stored in memory 212.

[0047] The process 5 includes a step 52 for calculating the fuel level in the tank, based on the numerical value of the capacity and a predetermined dielectric constant of the fuel stored in the memory 212 of the fuel gauge 20. This step 52 is performed by the microprocessor 211 directly in the tank 10, thus providing a reliable measurement of the fuel level, corrected using the predetermined dielectric constant value. At step 52, the fuel level can be obtained using the following formula:

[0049] With Hp being the height of the fuel-covered probe, C the capacitance measured by capacitor C1 when immersed in fuel, Cv the capacitance of capacitor C1 when empty (not immersed in fuel), Kf the dielectric constant of the fuel, and a a constant depending on the shape of capacitor C1. For example, for a capacitor C1 such as the one shown in Figure 5, which displays a schematic representation of a cylindrical fuel gauging capacitor with a concentric cylindrical inner and outer electrode, the constant a is calculated as follows:

[0051] With s0 the permittivity of free space approximately equal to 8.85, Ro the radius of the external cylindrical electrode and Ri the radius of the internal cylindrical electrode.

[0052] The fuel level in tank 10 is determined by gauge 20, which is fixed to the bottom of the tank. When tank 10 is empty, gauge 20 measures zero fuel level. When tank 10 contains fuel, the level measured by gauge 20 corresponds to its immersion depth. This immersion depth is the height of the fuel in tank 10 from zero, i.e., from the bottom of tank 10. Thus, the immersion depth of gauge 20 is approximately equal to the height of the fuel in tank 10 from the bottom of tank 10. When the fuel tank does not have a flat bottom, several gauges 20 may be present and measure different fuel levels. This point will be explained later in the description with reference to Figure 3.

[0053] The dielectric constant of the fuel can be obtained in several ways. The simplest method is to store a fixed dielectric constant in the memory 212 of the gauge 20. In this case, it is said to be "predetermined" because it is determined, prior to the height calculation, for example, by an operator. A second method of obtaining a dielectric constant, advantageous because it allows adaptation to the fuel temperature and the fuel in the tank 10, involves calculating this dielectric constant from a temperature measurement and / or a measurement obtained from a compensator. The calculation of this dielectric constant can be performed using publicly available charts (for example, CRC 663 from the "Handbook of Aviation Fuel Properties").These charts provide the value of the dielectric constant as a function of temperature for each fuel (for example, for the following fuels: JP-10, JP-8, Jet A, Jet A-1, etc.). For example, such charts are shown in Figure 6. In the invention, it is possible to use the line corresponding to Jet A-1 in Figure 6 to determine the dielectric constant of the fuel from its temperature. Jet A-1 is a fuel used in most commercial flights. It is also possible to use the line for any other fuel, provided it corresponds to the fuel in tank 10.

[0054] A compensator is a reference gauge located inside tank 10 and fully immersed in the fuel in tank 10. It allows the calculation of the fuel's dielectric constant because the compensator's immersion depth is known, its height being equal to the compensator's height. Thus, the calculated dielectric constant can be obtained using the formula:

[0056] The method 5 includes a step 53 for storing the fuel level calculated in step 52 in the memory 212 of the fuel gauge 21. This storage step is initiated by the microprocessor 211. Step 53 allows access to the calculated levels during probe maintenance, thus enabling the determination of the origin of a probe anomaly and its time of occurrence. In a preferred embodiment, at least one other metric or data point is stored in the memory. The stored data is at least one of the following: the measured capacitance of capacitor C1, the standard deviation of the measured capacitance of capacitor C1 over a given period, the fuel temperature measured by the temperature probe when present, the predetermined dielectric constant, or the calculated dielectric constant.

[0057] The process 5 then includes a step 54 of transmitting, in a digital signal, the fuel level calculated in step 52 and stored in step 53 to the external computing computer 30 located outside the tank 10. This step includes transforming the calculated digital level data into a digital signal by encoding. For example, such encoding includes modulation. The signal is then transmitted to the external computing computer 30 via the electrical harness 40, which connects the gauge 20 to the computer 30.

[0058] The computing unit 30 is external to the tank, meaning it is not contained within the tank's enclosure. The computing unit 30 comprises at least one processor and memory that stores instructions which, when executed by the processor, cause the processor to carry out the step associated with those instructions. Thus, when an action is assigned to the computing unit 30 or its processor, the processor of the computing unit 30 executes instructions stored in memory.

[0059] The computing computer is configured to implement steps 55 and 56 of process 5.

[0060] In step 55, the calculation computer 30 receives the digital signal containing the fuel level calculated by the gauge 20, possibly corrected for the dielectric constant when calculated. This reception step is possible because the calculation computer 30 includes at least one communication module, for example, an electrical connection or a network module, linked to the gauge. This communication module also allows the calculation computer 30 to control the gauge 20, for example, to request a fuel level reading. Alternatively, the gauge 20 can be configured to periodically transmit the calculated fuel level reading.

[0061] At step 56, the computing computer 30 calculates the quantity of fuel in the tank 10. To do this, the computing computer knows the geometry of the tank 10 and uses the received fuel level data to obtain the quantity of fuel in the tank 10. The computing computer 30 may, for example, know the geometry of the tank because it is predetermined and stored in memory, for example, in the memory of the computing computer 30 or in an accessible database. For example, the geometry of the tank 10 may be obtained using a lookup table between an identifier of the gauge 20 from which the digital signal received at step 55 originates, and a geometry of the tank 10 in which the gauge 20 is located.

[0062] In a preferred embodiment of the system according to the invention, schematically represented in Figure 3, the tank 10 comprises a plurality of gauges 20. Each gauge 20 of the plurality of gauges 20 is addressable by the computing computer 30 independently of the others, which allows the computing computer 30 to reconstruct an accurate geometry of the tank 10 and its various fuel levels, even when the bottom of the tank 10 is not flat or when the bottom of the tank 10 has different heights. Furthermore, this allows the computing computer 30 to perform a consistency check between the fuel levels received from the different gauges 20, adding an additional level of security to the invention.

Claims

DEMANDS

1. An aircraft fuel gauge (20) intended to be located inside an aircraft fuel tank (10), the fuel gauge (20) being configured to form at least one capacitor (C1) with fuel in the fuel tank (10), the fuel acting as the dielectric of the capacitor (C1), the fuel gauge (20) comprising at least one memory (212) and a microprocessor (211), the microprocessor (211) being configured to: - Convert (51) a measured analog value of capacitor capacitance into a digital capacitance value, - Calculate (52) a fuel height in the fuel tank (10), from the numerical value of capacity and a predetermined dielectric constant of the fuel stored in the memory (212) of the fuel gauge (20), - Store (53), in the memory of the fuel gauge (20), the calculated fuel level, - Transmit (54), in a digital signal, the calculated fuel height, to a computing computer.

2. Aircraft fuel gauge (20) according to claim 1 wherein the memory (212) is a non-volatile memory.

3. Aircraft fuel gauging system (S1) comprising: - A fuel tank (10) of the aircraft, - At least one fuel gauge (20) according to one of the preceding claims located inside the fuel tank (10), - A computing computer (30) included in the aircraft and located outside the fuel tank (10), configured to: o Receive (55) the digital signal including the calculated fuel height, o Calculate (56), from the fuel height and a predetermined geometry of the fuel tank (10), a quantity of fuel in the fuel tank (10).

4. System according to claim 3 further comprising a thermometer inside the fuel tank (10). [Claims] Aircraft comprising the system (S1) according to one of claims 3 or 4.

6. A method (5) for measuring the quantity of fuel implemented by a system (S1) according to claim 3 or 4, the method comprising: - Convert (51), by the microprocessor (211) of the fuel gauge (20), a measured analog value of capacitor capacitance into a digital capacitance value, - Calculate (52), by the microprocessor (211) of the fuel gauge (20), a fuel height in the fuel tank (10), from the numerical value of capacity and a predetermined dielectric constant of the fuel stored in the memory (212) of the fuel gauge (20), - Store (53), in the memory of the fuel gauge (20), the calculated fuel level, - To transmit (54), in a digital signal, the calculated fuel height to a computing computer (30), - Receive (55), via the computing computer (30), the digital signal including the calculated fuel level, - Calculate (56), using the calculation computer (30), from the fuel height and a predetermined geometry of the fuel tank (10), a quantity of fuel in the fuel tank (10).

7. Method (5) according to claim 6 implemented by the system (S1) according to claim 4 wherein the predetermined dielectric constant is calculated by: - Obtaining a temperature reading from the temperature sensor, - Calculation of the predetermined dielectric constant from a dielectric constant of the fuel and the temperature obtained.

8. A method (5) according to claim 7 further comprising: - A storage step, in the memory of the fuel gauge (20), a data history including at least one of the following data: capacity, standard deviation of capacity over a given period, fuel temperature, predetermined dielectric constant, calculated dielectric constant.

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